Gear type tools such as a gear type grinding wheel and a shaving cutter are known as tools for use in the finishing operation of gears. In these tools, the tool is brought into engagement with the gear to be worked and with a suitable shaft angle defined therebetween. The working operation is performed by rotating either the tool or the gear. During this operation, the tool and the gear are caused to slip between their engaging surfaces, and thereby undesirably grinding or cutting the toothed surface of the gear.
By way of example, FIG. 3 illustrates a gear type grinding wheel (to be merely referred to as a "tool" hereinafter) in a partly cross-sectional view, whereas FIG. 4 illustrates the working teeth of the gear in perspective. The tool 1 in the illustrated example has gear-shaped working teeth 3 formed integrally with and on the outer circumference of the base metal 2 and hard grains secured over the inner grinding toothed surface 4 of the gear 3 through an electrodeposition and the like. The base metal 2 is formed by coupling a boss portion 6 for engagement with a tool-mounting shaft 5 (shown by a double-dotted chain line) and and a rim portion 7 having working teeth 8 formed therein, integrally with each other through a disk-portion 8, and manufactured through a turning operation.
In general, a cutting oil is sprayed toward a working station so as to dissipate frictional heat and remove chips produced during the grinding operation.
Because the tool 1 is caused to rotate in engagement with the gear, i.e., working at a fast speed while the above-described gear type tool is being operated for a working purpose, it is extremely difficult for the cutting oil to be fed to a grinding point exactly on the toothed surface, because the oil tends to be dissipated under the effect of centrifugal forces among others, and thereby causing a plug-up of the tool 1 and the like at its toothed surface 4. As a consequence, precise performance characteristics of tools tool available for grinding operation have been impaired.
To eliminate such drawbacks, a gear type grinding tool (shown in FIG. 5 and FIG. 6 generally in cross-sectional view and a pespective view for the tool) has been proposed in a prior art such as those disclosed in the Japanese Patent Application Disclosure No. SHO 63-16921 Official Gazzette. In this tool, an oiling path 9 is provided in the interior of the tool-mounting shaft 5 and a grinding oil is designed to be supplied under pressure toward a multiple of holes 10 defined through the toothed surface 4 of the grinding tooth 3 from the oiling path 9 so that the grinding point may be directly supplied with the grinding fluid. However, it is very difficult to manufacture such a tool practically, and additionally a substantial cost is needed for carrying out such manufacture. The tool is designed such that the grinding oil is supplied from the interior of the tool-mounting shaft 5 under pressure, and thus the oiling mechanism becomes complicated.